I don't have many more ideas than RonaldPR. As long as you've verified that the executable bits are not set and that Play is the default application, the only other thing I can think of to try is to delete Play and reinstall it. It is possible that one of the icons became corrupted (you can always open the Play.app folder and look at the icons inside it, along with Info.plist to see which icon is being mapped to .flac files).

Which Play version do you use? I use the latest 'unstable' version r1077. Maybe installing that one solves the problem.http://forums.sbooth.org/viewtopic.php?f=14&t=1895
(For these builds, 'unstable' does not really mean they are unstable, just that it is not yet a release version. The fact that this is the latest version since February 8th, indicates that there was no urgent reason to make changes and that it is safe to use.)

RonaldPR wrote:I use the latest 'unstable' version r1077. Maybe installing that one solves the problem.

sbooth wrote:It is possible that one of the icons became corrupted (you can always open the Play.app folder and look at the icons inside it, along with Info.plist to see which icon is being mapped to .flac files).

I downloaded both the latest stable and the r1077 version (still not installed them as I'm presently away from the computer) and looked at their contents. There are seven .icns files in Play.app/Contents/Resources, namely AIFF.icns, Generic.icns, Library.icns, MP3.icns, Ogg.icns, Play.icns, and WAV.icns. Notice that there is no ICNS file for FLAC!

(As I wrote earlier, when I right-click on a FLAC file and select Play as an application to always open the file with (so there is no Get Info dialog), a score icon is set for that particular file. I now see that this 'score' icon is the Generic.icns.)